The present invention relates to a drilling tool for the chip-breaking machining of metallic materials, especially for so-called ejector drilling. However, it may also advantageously be used for so-called BTA-drilling.
It is known to use cutting inserts of cemented carbide for drills, which inserts are fastened by mechanical fastening arrangements, the inserts being provided with one or more recesses in the chip surface for chip-breaking purposes. Such drills are, for instance, known from U.S. Pat. No. 4,215,957. However, it has turned out to be difficult to attain an optimal forming of the chips. That is, it has been impossible to attain the desired short, comma-shaped chips, at the same time as it has been impossible to reduce power consumption when running the drill in the desired way.
Further, in U.S. Pat. No. 5,302,060 drilling tool is described comprising a drill body on which two or more cutting inserts are mounted. The inserts are substantially formed as trapezoids and are axially mounted, i.e., the abutment surfaces of the cutting inserts extend axially, the inserts suitably being fixed by brazing. This makes the brazing of the inserts more difficult, since accessibility to the inserts in the axial direction is considerably reduced in the chip flute or canal. Moreover, during manufacture of the drill body it is difficult to position a milling tool downwardly into the chip flute in cases when the insert seats or pockets are to be milled out. A further drawback with this construction is that the axial extension of the inserts are bulky and that the chip flutes or canals become long, and this increases the risk of chip jamming. Furthermore, the long chip flutes have the consequence that one has to mill relatively deeply, with large over-hangs resulting.
In U.S. Pat. No. 4,768,901 a drilling tool is disclosed having a tangential positioning of the drilling inserts on the upper or end-side of the drill head. Admittedly, this has made possible shorter chip flutes and, consequently, a decreased risk for chip jamming. On the other hand, the drill inserts and/or the tangential insert seats is/are unnecessarily complicated. Thus, the inserts shown in FIG. 3 of this citation are apt to break, on one hand because of the included 90.degree. angles which function as kerfs, and on the other hand because of the complicated geometry, which causes compacting problems when the inserts are pressed. Moreover, the formation of insert seats necessitates a relatively complicated and very precision-demanding milling operation in order to obtain a satisfactory abutment of the seat against the insert, particularly since the latter is fastened by screws and not by solder.
Thus, a primary object of the present invention is to provide a drilling tool that is easy to manufacture.
A second object of the present invention is to simplify, as far as possible, the production of the insert pockets in a drill head, particularly in an ejector drill head, and also simplify the production of the cutting inserts, particularly by avoiding all compacting problems when pressing them.
Another object of the present invention is to reduce the number of different cutting insert designs to a minimum, in particular to only one design.